Used to get slick ads for nightclubs and events from promoters with the red squiggles printed on them. Nice, full color, glossy, 4x6 card size ads that they'd stick on car windshields, hand out on the street, and stuff into any nook or cranny they could find. I was somewhat mystified as to what production process they used that allowed for the squiggles to remain and why what they were trying to indicate was ignored as most of the errors were indeed errors. Simply sending a document to a print device normally does not preserve the squiggles but somehow, they would end up in the adverts.